Chapter XIII of the 1978 Constitution provides that the President may submit by referendum to the people, with the approval of the Cabinet of Ministers or the Supreme Court, any bill, provision or matter of national importance. Additionally, the President may in his discretion submit to a popular referendum any bills rejected by the Parliament insofar as they would not modify, repeal or replace the current Constitution. A bill is considered to be adopted by referendum if a majority of voters cast their votes in favor and if at least two thirds of registered voters participated in the referendum. If the participation is below this threshold, a bill is adopted if at least a third of registered voters cast a vote in favor of the bill. Some dispositions of the current Constitution are entrenched clauses, meaning that they can only be revised with both the approval of Parliament through a two thirds majority and the approval of the people through a national referendum. Article 83 of the Constitution provides a list of these entrenched clauses requiring popular approval to be repealed or replaced. Referendums are to be organized by the Commission of Elections and further regulated by the Referendum Act, No. 7 of 1981. So far, only one national referendum has taken place in Sri Lanka since independence. In 1982, newly elected President J.R. Jayawardene called a referendum to extend to mandate of Parliament for six years, in order to maintain the comfortable majority of his United National Party in the legislature. Despite claims of authoritarianism by opposition parties, voters decided to extend the life of parliament by over 54 percent of valid votes. Another referendum may be organized in the coming months or years to validate the outcome of the constitutional process initiated by President Maithripala Sirisena after his election in 2015.
Sources:
1978 Constitution of Sri Lanka, Chapter XIII: The Referendum